The pack as shown is a 16s2p (48volt 20ah) pack of Headway cells. The cells were bought last year via a group purchase deal ... There has been a continuing issue with this pack where cells are dying and I've never gotten to use any of it to power a vehicle. Well, until today that is. It arrived with funky packaging and one cell pair dead and some of the BMS wires were loose (bad soldering). I eventually bought another cell pair and by the time (months later) I got it rearranged other cell pairs had died. I bought some more cells and also redid all the BMS wires to have better connection. FWIW The resulting pack has cells with manufacturing dates spread out over the last 1+ year.

A couple weeks ago the pack came together as shown in the picture. All the cells were full (3.2-3.3 volts) and I left it sitting. Then yesterday I wanted to mount it on the bicycle and started checking the cell voltages. Some of the cells (2 pairs) were dead. I'm really getting tired of this.

I took off the BMS completely as I'm totally not confident in it. I've heard from others that BMS may be problematic.

Unfortunately I don't have enough cells for the 48v 20ah pack. So I redid it to a 10ah pack (16s1p) w/ no BMS at the moment. It was enough to put it on the bike and take it around the block a couple times. The bike is great, powerful, etc. I think there's only one kink left - the lights aren't working right. But this is about the pack.

My options are:-

a) get a few more cells to get it back to a 48v20ah pack - PLUS - get the fetcher/goodrum BMS (I found the place that sells assembled BMS boards)

b) leave the 48v10ah pack as is and use some of the cells to make a 24v10ah pack for another of my bicycles, that bike has a 24v10ah pack already but that pack isn't quite strong enough for the discharge on that bike and adding another 10ah of cells would make that bike more useful

b.1) also get the fetcher/goodrum BMS board

c) forgo the BMS entirely and just be careful on the monitoring

One thought is maybe these headway cells I have are just bad anyway. They keep dying and maybe throwing more money at them (buying a this other BMS board) is just throwing good money after bad. Option (c) is my frustration plan.. I just use the cells as is until they all die (assuming they're all going to die) and "later" buy a real pack from a reliable manufacturer. Basically I have no idea whether to trust these headway cells at all.

Which BMS did you get with the pack? We are finding that some of the 3rd party BMS systems Headway packages with their cells are junk and quit selling them too. The cells are all fine. The BMS boards are killing them. I also do not like any of the packaging I have seen directly from Headway. However the cells are still testing to my liking :-)

I have found it wise to periodically TEST the BMS (battery management system) to see if any section is discharging a cell that should not be discharging-that is, if a cell with equal, or lower, voltage to the other cells is being discharged, there is a BMS problem! How do you do this?--Simply use a voltmeter, and check for voltage at each cell balancing load resistor-these resistors are provided for each cell, and are normally of a larger size and lower resistance than the others on the board. Typical values are in the 3 to 75 ohm range, depending on the size cells the board is designed for. (Bigger cells, lower resistance, usually.)-I had an "Inductive Current Spike" cause a BMS to fail, and continue to draw down a lithium polymer cell, even though the cell was not at excess voltage level. Luckily I found the problem before the cell was destroyed.-You may need to add supression of such short duration, high-frequency voltage spikes to your assembly, doing so is a good idea anyway, as it reduces the possibility of Radio Interference both to anf from your circuitry. It is easy for most D.C. circuits to momentarily generate voltage spikes that are at least 2 or 3 times battery voltage, whenbswitching, pulsing, or disconnecting a load. Use of proper "Snubbing Networks" overvoltage varistors, zener diodes, current limiting resistors, bypass capacitors, RFI shielding, and suppression chokes/inductors can improve circuit reliability. (Don't be a "Runaway Toyota"!)-Bob Curry

Which BMS did you get with the pack? We are finding that some of the 3rd party BMS systems Headway packages with their cells are junk and quit selling them too. The cells are all fine. The BMS boards are killing them. I also do not like any of the packaging I have seen directly from Headway. However the cells are still testing to my liking :-)

Mike

There's no labeling on the BMS board but you can clearly see it in the picture above.

As said - the pack came through the group purchase Joshua organized 1.5 yrs ago. We thought we were dealing directly with Headway but turned out to be a third party. And yea the packaging it arrived with was more than funky.

Hmm.. buying two more cells would get me back to a 20ah pack and then the fetcher/goodrum BMS board ..

For the record - I decided on choice (a). At http://kenalten.com they have cells at a good price and Ken promises they're in stock and can ship right away. Further they have a BMS at a reasonable price and which Travis (aka Frodus) recommends. Since Travis is the Headway expert at EV Components I'm trusting his opinion on this. Just looking at their website it doesn't say enough to convince me their BMS is better or worse than anybody elses. But I know and trust Travis.

I have had 12 of 48V20AH Headway packs for a few weeks now waiting to go into a car. From the time they were made until now is about 8 weeks and I measured every pack when I got them and about 3 days ago to ensure they were at least showing reasonable terminal voltage with no load.
All 12 measured 53.4 volts.
The BMS with them is a Headway BMS WL086-05.

So far so good.
The cells are fine but it sounds like your BMS is discharging and destroying them.

Did you resolve your BMS issues? I have been using the Signalab BMS V2 (SMD LEDS) with my 16s2p pack. Works flawlessly with about 75 cycles to date. I balanced the cells to 3.3 volts first (put all in parallel with a single cell charger). All cells balance within 1-2 minutes (LED's go (shunt) on and then off). I think I only paid $80 for the BMS.

No.. I never did. I ended up running the pack w/o BMS for a while and couldn't trust myself to trust any of the affordable BMS's I found out there. Unfortunately I accidentally fried the pack. At the same time I have these pingping packs I bought 3 yrs or so ago and they're still going fine, and I see with a bit of searching that it's Signalab that pingping used. That's piqued my interest..

Just like to add here that Ive used 10amphr Headway cells for 2 years now (without a BMS) on a few bikes and they are all fine.
I like Headway cells as they are easy to bolt together. I series charge and they dont get that out of balance without a BMS, and it saves all those wires, ocassionally I do manual individual cell checks to make sure they are level.

I add this here because if I was converting a Vectrix to Lifepo4 I think I would use Headway cells , they are only $18 each and so 40 would cost about $700.

p.s. Tip, heres a trick, cut the heads of 6mm bolts and use them to connect the headways in lines with no gaps or wires inbetween.
For 48v system have 4 lines of 4, or if you have the room 2 lines of 8. Put these lines in alternating diections and then you only need one short copper bar to connect the strips!

I got mine from hightekbikes. Ping may sell them as well, he claims to make them. I'd never run without a bms, the curves at both ends are way too steep to chance it. Besides, if you're canstantly monitoring and worrying obuot each cell your not running without a bms...YOU are the bms.

Yes, when I first bought my cell's I was hoping to go "bare back" as well, but after bench testing I found that during charging the headway cells could go from 3.6 to over 4 volts in seconds....even after matching them prior to. The first 4-5 times I charged I'd watch them all blink into shunt and then turn off my charger. Been over 70 cycles now and no issues....does its job, cheap and you don't have to build it. Theres a schematic floating around too, some have upgraded the output FETS and lowered the shunts R to increase its 30 amp output to 80amps.

I agree, Haedway without a BMS is a bad move. I recently charged my spare cells and while all went to 3.65 V in about the same time, one happily went to 4V in about the next minute while the other two (only have 3 spares at the moment) really wanted to be pushed to go above 3.7V.
Getting the odd cell to destructively high voltage is all too easy. Cells are 38120S.

Ahhhhh that explains it, Ive been wondering why some guys are having fried cells and Ive never had that problem, You're not giving your cells enough leeway.
On my 48v bike which has 16 HEADWAYS, I series charge to 57.4V - Thats about 3.59v per cell.
Maybe every 5 charge cycles or so, I use a meter to check each cell voltage. If there are any that are lower than 3.59v after charging light goes green, I give them an extra few minutes with a single cell charger until they reach that.

Never had a problem.

This obsession with driving the cells to 3.7v would give you at most 2% more energy than stopping at 3.59v, but totally removes your margin of error - as correctly pointed out the voltage raises sharply from 3.65v upwards.

Incidentally 57.4v charge end works out well too because its the max my old 48v SLA charger was set to - so it really is quite easy!

Your not frying your cells because of a combination of luck and manual monitoring. You've been lucky to catch the low ones by monitoring them and then manually bringing them into balance with the pack....if not the low ones would force the higher ones over 4v and into failure....your pack would have been dead by the 3rd of 4th cycle. Your not runnng without a BMS...you just choose to be a low tech BMS. I couldn't be bothered with opening my pack and checking 16 cells and then single cell charging....perfer they work just like the LI batts in my cell phone and laptops. Plug in the charger and walk away knowing the BMS is doing the job. I use a 48v, 4 amp scooter charger intended for AGMS and signalab V2.5 BMS.

Not quite, because one low cells deficit will be averaged out over 15 others.
E.G. say theres a low cell 3.3v (never had one that far out) but even then this .29v difference will be shared out amongst the other 15 cells which would then read 3.61v (no where near 4v)
As soon as the low cells topped up the next series recharge will leave the all back at 3.59v again.

My cells are easy to access, but as an experiment I wont manually rebalance any low cells for the next few weeks and Ill report back how far out of balance they go. I use and recharge the bike daily so will feedback in a couple of weeks!

Don't get me wrong, if you don't mind watching your cells and balancing them manualy thats just fine... with great care and some luck you may not kill any cells. Just doesn't change the fact that Li cells WILL go out of balance with normal use and WILL fail if overcharged or under discharged AND because of this they REQUIRE a BMS of somekind (even if its a human one with lots of free time). Some of those less festidious do/will kill expensive cells or packs going "bare-back". Soldering 14 extra little wires ONCE doesn't take that long in comparison. Fortunately there are some low cost and high quality BMS systems out there now for us DIY guys. Unfortunatly, some of the junk ones (like Headways 1st BMS) left a bad taste for Lifepo4 and BMS.

Thats not true at all....impedance will be no help if you discharge below 2v long enough. And even cells with matched Z's will change over time and load.

I see you posting about CHL battery but were can they be bought? Website? Nothing but talk it seems? Also, if you want to impress people, show them a 4 or 5C discharge curve. A static Z reading means very little....for example A123's are rated at 7mohm...they are 35C cells. You say CHL is .31mohm? What is the C rating? See, static Z means very little.

I just bought 26 Calib 40ah's.....if I knew more maybe I would have bought CHL? If these batteries really do 6C they would be very useful for Motorcyles in the 40ah version.

But my company are focus on china domestic market with a lot of government incentive policy on EV,especially that we are main supplier for biggest hybrid E-bus in Asia,Kinglong bus.

Export business just new start,so that our website don't have English vesion,pls be considerate.

We don't have machine to get 5C discharged curve,but our 40AH battery really under 5C big load of hybrid bus.And even 5kw to 8kw electric scooter testing,it is only very little drop on voltage when full throttle.

@Johny - yes I will act with caution, will still monitor although I wont rebalance while Im doing the test. I think your web blog is very good, it has lots of clear photos - I want some of those battery terminal connector lugs and one of those mega crimpers! Whats the website for the Toolbox place you said you bought those lugs from?
I think I should return the words of caution with a warning about 600v systems - Dont you feel nervous working with voltages that can arc insulators??

@CHL, whats your price for 20ahr cells?
I bought some from Yesa last year and they are good (can do 5C without too much voltage sag) but they were quite expensive

But my company are focus on china domestic market with a lot of government incentive policy on EV,especially that we are main supplier for biggest hybrid E-bus in Asia,Kinglong bus.

Export business just new start,so that our website don't have English vesion,pls be considerate.

We don't have machine to get 5C discharged curve,but our 40AH battery really under 5C big load of hybrid bus.And even 5kw to 8kw electric scooter testing,it is only very little drop on voltage when full throttle.

You welcome to start with sample testing !

Sorry, but I can't believe a manufacture of batteries won't have 1. A website and 2. an active load capable of 5C. Does your company own a volt meter??

If you don't believe,welcome to china or your friend welcome to china and confirm !

We have 1C discharge machine and I also post the curve on another topic. But very rare chinese lithium battery have 5C discharged machine,if you are professional enough,you can find the discharged rate from high power electric motorcycle which normally 4C or 5C on controller.

Joe, lets wait until you post some 5c data. Also more info on your company, do you take credit card? how long for shipping, any referances? We want to see how your product and company compare with Calib & Winston? Calib now has a site in Ca, I ordered 24 cells last Wensday, they are due on tomorrow plus they take CC so it is mush safer then sending money to China.